The method and apparatus of the present invention relate generally to testing micro electromechanical relays. More particularly the method and apparatus of the present invention relate to testing quality and reliability of micro electromechanical relays.
In the past few years, many micromechanical and micro electromechanical devices (hereinafter collectively referred to as “MEMs devices”) that include mechanical members have been made from silicon or other etchable materials using fabrication processes and equipment that are developed for standard semiconductor integrated circuit chips. These MEMs devices are advantageous because they be made with microfabrication techniques having increased precision, allow for smaller miniaturization, and generally have lower power requirements.
One of the MEMs devices being actively pursued by IBM is the MEMs-based relay for application in the radio frequency (or RF) communication technologies. This is because the switching characteristics of a MEMs relay is superior to those of traditional switches like the GaAs MESFET, and the p-i-n diode. For example, MEMs relays have much lower power consumption rates, lower insertion losses, and much higher linearity. All these features make MEMs relays a great candidate for wireless communication applications like a wireless transceiver in a cellular phone.
A MEMs relay is simply a miniature mechanical switch that switches on and off in response to a DC voltage bias actuation. When a DC actuation voltage is applied, the electrostatic force changes the switch position to make contact between the RF signal electrodes that results in an ohmic contact to allow the RF signal to pass through. To further reduce the insertion loss and improve the switch linearity, the RF signal electrodes are separate from the DC actuation electrodes.
Although the development of MEMs devices having etched mechanical members has been expanding, several manufacturing problems have not yet been adequately addressed. For example, one problem is testing the MEMs devices to qualify a MEMs device for a user's particular application to ensure that the devices provide the desired operational and performance characteristics. It is typically desirous to execute a series of stresses and measurements on samples of the proposed devices so that quality and reliability can be evaluated prior to user implementation. Cost and schedule advantages are achieved by stress testing in identifying only good performing devices worthy of investment for assembly, and quantifying device performance at completion of fabrication (thus communicating device characteristics at completion of fabrication, unmasked by further assembly effects).
Prior art MEMS switches require a large voltage to actuate the MEMS switch. Such a voltage is typically termed a “pull-down” or “pull-in” or actuation voltage, and, in the prior art may be anywhere from 20 to 40 volts or more in magnitude. To explain further, a typical MEMS switch uses electrostatic force to cause mechanical movement that results in electrically bridging a gap between two contacts such as in the bending of a cantilever. In general this gap is relatively large in order to achieve a large impedance during the “off” state of the MEMS switch. Consequently, the aforementioned large pull-down voltage of anywhere from 20 to 40 volts or more is usually required in these designs to electrically bridge the large gap, while a smaller maintaining voltage may be employed to maintain the bridge. Also, a typical MEMS switch has a useful life of approximately 108 to 109 cycles. Thus, in addition to the above concerns, there is an interest in increasing the lifetime of such MEMS switches.
Thus, there is a need for a method and apparatus for the purpose of performing a quality and reliability study of a proposed MEMs switch that has the ability to measure basic device parameters, such as pull-down, activating or actuating voltage, drop-out voltage, contact resistance and their impact on the switch lifetime.